Recently, there has been an increasing interest in energy storage technology. Electrochemical devices have been widely used as energy sources in the fields of cellular phones, camcorders, notebook computers, PCs and electric cars, resulting in intensive research and development into them. In this regard, electrochemical devices are one of the subjects of great interest. Particularly, development of rechargeable secondary batteries has been the focus of attention. Recently, research and development of such batteries are focused on the designs of new electrodes and batteries to improve capacity density and specific energy.
Many secondary batteries are currently available. Among these, lithium secondary batteries developed in the early 1990's have drawn particular attention due to their advantages of higher operating voltages and much higher energy densities than conventional aqueous electrolyte-based batteries, for example, Ni-MH, Ni—Cd, and H2SO4—Pb batteries. However, such lithium ion batteries suffer from safety problems, such as fire and explosion, when encountered with the use of organic electrolytes and are disadvantageously complicated to fabricate. In attempts to overcome the disadvantages of lithium ion batteries, lithium ion polymer batteries have been developed as next-generation batteries. More research is still urgently needed to improve the relatively low capacities and insufficient low-temperature discharge capacities of lithium ion polymer batteries in comparison with lithium ion batteries.
Also, for the development of a cathode, anode, separator and electrolyte solution comprised in lithium secondary batteries, various additives are used therein. The additives are largely divided into essential additives which are required in the operation of batteries, and additional additives which are further used to ensure the performances and safety of the batteries. Generally, the former essential additives are used in the preparation (manufacturing) of battery components, while the latter additional additives are used in the preparation of the battery components or in the assembling of batteries.
Among such additives, additives for ensuring safety are required in a certain moment, for example, when an overcurrent or high temperature state occurs due the abnormal operation of batteries, while some additives are continuously required in a certain degree during the use of batteries.
Particularly, some additives are intended to activate during the operation cycles of secondary batteries to remove capacity-fading factors and implement more stable cycles. However, since these additives may cause other side reactions, it is important for them to be placed in a suitable position at a required time.
Meanwhile, most of additives for improving cycle performances are focused on an electrolyte solution, cathode and anode. Accordingly, there is need to develop a method for maintaining additives in an efficient position while taking into account a side reaction due to the additives.